Notwithstanding the league's founding, as had the founding of the Protestant Union, it further exacerbated long standing tensions between the Protestant reformers and the adherents of the Catholic Church which thereafter began to get worse with ever more frequent episodes of civil disobedience, repression, and retaliation that would eventually ignite into the first phase of the Thirty Years' War roughly a decade later with the act of rebellion and calculated insult known as the Third Defenestration of Prague on 23 May 1618.

In 1555, the Peace of Augsburg was signed, which confirmed the result of the Diet of Speyer (1526) and ended the violence between the Catholics and the Lutherans in the Holy Roman Empire.

Further, Calvinism spread quickly throughout the Holy Roman Empire, adding a third major Christian worldview to the region, but its position was not supported in any way by the Augsburg terms, since Catholicism and Lutheranism were the only permitted creeds.

The best documented reason of the foundation of the Catholic League was an incident called the Kreuz- und Fahnengefecht [de] (lit.

The Catholics, led by five monks, wanted to pass through the town and on to the nearby village of Ausesheim, showing their flags and singing hymns.

Nevertheless, next year similar anti-Catholic incidents of civil disobedience took place, and the participants of the Markus procession were thrown out of town.

On 10 February 1610, the representatives of all the important Catholic states, except for Austria and Salzburg — and a great number of the smaller ones — met at Würzburg to decide the organization, funding and arming of the League.

To prevent him from doing so, Spain, which had made the giving of a subsidy dependent on Austria's enrollment in the League, waived this condition, and the pope promised a further contribution.

The membership of the Habsburg monarchy made the League part of the struggles between the emperor and his Protestant vassals in Bohemia and Lower Austria, that would lead to the beginning of the Thirty Years' War.

Duke Maximilian refused to accept the resolutions of Ratisbon and even resigned the post as president, when Archduke Maximilian III of Austria, the Prince Elector of Mainz and the Prince Elector of Trier, protested the inclusion of the Bishop of Augsburg, and the Provost of Ellwangen in the Bavarian Directory.

Already having been crowned King of Bohemia in 1617, Ferdinand II and his Catholic governors were deposed by rebelling Protestant Czech nobles in the second defenestration of Prague in 1618.

Based on the terms of the treaty, Maximilian, leader of the Catholic League, made his Bavarian forces available to Emperor Ferdinand.

With 7,000 men, Bavaria supplied the largest contribution to the army, whose strength was fixed at Würzburg in December 1619, as 21,000 infantry and 4000 cavalry.

Tilly won the Battle of White Mountain north of Prague on 8 November 1620, in which half of the enemy forces were killed or captured, losing only 700 men.

When another Protestant army under Georg Friedrich, Margrave of Baden attacked on May 6, Tilly's League force convincingly won the Battle of Wimpfen, scattering the enemy.

After that battle the Protestant forces still fighting for Frederick V of the Palatinate withdrew over the Rhine and allowed the Catholic League army freedom of action.

With the exception of the still besieged fortress of Frankenthal, the Electoral Palatinate was occupied by League forces while Count Frederick was in Dutch exile.

This caused Denmark's king Christian IV to enter the Thirty Years' War in 1625 to protect Protestantism and also in a bid to make himself the primary leader of Northern Europe.

Supported by the Catholic princes and their victorious League army, the emperor now moved to denounce Protestantism as illegal in many territories of Northern Germany.

It was specifically aimed at restoring the situation of the 1555 Peace of Augsburg in ecclesiastical territories that had strayed from "legal" Catholic faith and rule, in the decades since then.

Afraid that the Catholic League's army would be sent to enforce this new law, if challenged, their protestant authorities again looked abroad for allies to protect them.

The Peace of Prague of 30 May 1635, was a treaty between the Holy Roman Emperor, Ferdinand II, and most of the Protestant states of the Empire.